1. Field of the Invention
The present invention relates to a data processing system with virtual machines. More particularly, it relates to the determination of execution of control register load/store control instructions, by hardware in the system.
2. Description of the Prior Art
Large-scale computer systems frequently utilize the concept of virtual machines. Such systems are provided with a plurality of operating systems for controlling the virtual machines and with a supervisory operating system, i.e., a control program. The control program runs an actual machine, while the operating systems run under the control program.
Such a system may, for example, be provided with 16 (2.sup.4) control registers, if four-bits are provided in an instruction for selecting the control registers. Not all the 16 control registers, however, are initially defined and only the initially defined control registers may be repeatedly provided in the hardware of the system. As a result, when a new function is added, it is necessary to change the hardware if additional control registers are required.
Various proposals have been made to allow additional control registers to be defined in a main memory storage without adding hardware. However, such additional control registers cannot be accessed directly by the operating systems. Therefore, when any one of the operating systems generates a control register operating instruction such as a load instruction or a store instruction, an interruption is generated in the control program and control is transferred from the operating systems to the control program. In other words, such a control register operating instruction is simulated by the control program. This, however, increases the overhead time of the system.